An application for multi-module weighing systems is in automated production- and testing plants. Balances of a modular design—so-called weighing modules—are themselves particularly suitable for integration in these plants. In essence, these weighing modules are balances in which the display unit is arranged separately from the balance, for example in a system with a central display for a plurality of weighing modules. Areas of application for weighing modules of this type which are integrated in a system are installations for the production and testing of small, relatively expensive parts, for example filling- and packaging machines for tablets, capsules, vials, etc. in the pharmaceutical industry, or in the checking of ball bearings. The weighing of objects of the same kind or also the so-called batch-weighing are processes in which a plurality of material quantities have to be weighed individually within a compact space for purposes such as checking, dosage preparation, filling, etc.
Systems of this kind which are used to weigh objects of the same kind are known in the existing state of the art. They are configured primarily as linear or two-dimensional arrays of weighing modules. Other arrangements are based on a concept of placing the weighing modules in a two-dimensional arrangement like satellites around a linear arrangement of load receivers which will need to be adapted to the distances between the delivery elements of an existing transport conveyor device.
Other devices have compact weighing modules which are arranged at fixed intervals from each other in a shared holding structure, wherein the distance between them is kept as small as possible.
The weighing results as well as the reproducibility of an electronic balance or a weighing module are also influenced by the temperature of the weighing module. In the interest of reproducible weighings, it is therefore advantageous if each of the weighing modules arranged in a multi-module system has a substantially uniform operating temperature.
As the individual weighing modules in a multi-module weighing system are spaced very closely, this can cause a disadvantageous temperature distribution within the system, which can affect the reproducibility and repeatability of the weighing results of individual weighing modules and/or of the entire system.
In addition to the thermal effect that the weighing modules have on each other, fluctuations of the ambient temperature, in particular unexpected temperature peaks, can also have an influence on the zero-load indication, the reproducibility as well as other weighing parameters. Fluctuations of the ambient temperature in a production facility can be caused for example by machines being switched off, air-conditioning systems, radiation from the sun or other factors. However, especially in a production facility it is important for a balance to constantly be in a ready-to-operate condition without requiring long phases of adaptation to the ambient temperature while maintaining a uniform quality of the measuring results.
The state of the art in weighing technology offers a variety of cooled weighing compartments for a balance. The temperature control of the weighing compartment of a balance as disclosed in EP 1 396 711 B1 is achieved by using a temperature gradient which propagates along a vertical wall that is part of the stationary part of the balance and is connected to a thermoelectric module.
A balance with a weighing compartment is also disclosed in JP 2024518 A, wherein a heat pipe that is arranged in the housing part containing the electronics carries the heat being generated out of the housing to the outside, so that a temperature rise of the weighing compartment from the heat generated by the electronics is reduced.
In JP 2586115 B, a balance is disclosed whose weighing compartment is temperature-controlled by means of a thermoelectric module arranged in the weighing compartment in order to avoid convective air currents caused by opening the draft shield. This module is in thermal contact with a cooling plate which extends along the wall that separates the weighing compartment from the balance housing in which the electronics are enclosed or which is constituted by the separating wall itself. Its purpose is to keep the heat generated by the electronics of the balance from reaching the weighing compartment.
However, all of the foregoing solutions relate to balances with a single weighing cell, for example analytical balances, which have a weighing compartment enclosed by a draft shield. Usually, only the heat generated from the electronics of the balance is carried away or kept away from the weighing compartment, and no thermostatic temperature control nor a temperature adaptation to the ambient temperature is being performed. Especially an analytical balance is normally used in an environment whose atmospheric parameters are largely kept constant. In the case of an analytical balance it is therefore sufficient to switch the balance on with a certain lead time and to wait until the balance has reached its operating temperature or has taken on the ambient temperature.